Typically, aerosol valves for dispensing a moisture reactive composition in aerosol form such as a polyurethane foam are fixed to a pressurized can by a cup closing the top opening by means of a peripheral annular channel encasing a peripheral can bead defining the perimeter of the can top opening. The cup comprises a central bore through which a tubular resilient grommet extends both above and below the cup (the expressions “below” and “above” the cup refer herein to facing inside and outside the can, respectively). The grommet is roughly a hollow cylindrical tube which central bore opens at both ends and which comprises at its end located below the cup a substantially annular flange radially extending outwards and which upper surface contacts the lower (inner) surface of the cup and is suitable for sealing against the latter.
A rigid valve stem is engaged snugly in the central bore of the grommet extending both below and above said grommet and is held in place by appropriate means (generally annular flanges sandwiching the upper and lower portions of the grommet). The valve stem is formed by a hollow tube closed at a first end by an annular base forming a flange of diameter greater than the one of the inner bore of the grommet and which upper surface of the base flange is suitable for sealing against the lower surface of the grommet flange. The lateral wall of the tubular portion of the stem generally comprise openings bringing in fluid communication the inner bore of the stem with the interface between the stem base and the grommet flange.
By tilting the portion of the valve stem extending out of the grommet the sealing interface between the grommet flange and the valve base is disrupted thus bringing in fluid communication the inner bore of the valve stem with the composition contained in the can. Since the can is pressurized, the content of the can is dispensed through the valve. When closed, the valve must ensure that no moisture from the outside contacts the content of the can, if the composition is reactive to moisture. Examples of valve designs suitable for dispensing a pressurized composition reactive to moisture, such as a polyurethane foam can be found in WO2006/032061, U.S. Pat. No. 6,425,503, U.S. Pat. No. 4,765,516, EP0.102.797, WO2009/042206, WO96/17795.
This type of cans and valve systems is for example, widely used for polyurethane foam compositions, They are generally sold in rather small format, typically 1 liter cans or less and are disposable. This means that the cost ratio between container (=can) and content (=PU foam) is quite critical and any improvement towards a reduction of the former is beneficial to both consumers and foam producers, provided the reliability of the valve is maintained. This can be achieved by reducing the thickness of the can walls, in particular the cup thickness, but since the cans are pressurized, this solution is rather limited for obvious mechanical reasons. Furthermore, the tightness of the contact surface, on the one hand, between the upper surface of the grommet flange and the lower surface of the cup and, on the other hand, between the lower surface of the grommet flange and the upper surface of the valve stem base are critical to prevent any leak either of composition leaking out of the container or moisture leaking into the container. Moisture can penetrate into the can in particular during use of the can as the valve is being tilted because, in case the grommet is not stable enough, the seal between the grommet flange and the cup bottom surface can be momentarily disrupted. Furthermore, after a few tilting of the valve, some crazes may form in the grommet where it contacts the edge of the cup bore.
The moisture problem is addressed in U.S. Pat. No. 4,765,516, wherein the cup comprises an annular rib of radius less than the grommet flange radius, thus forming with the latter an annular channel in which any moisture that would have leaked through the interface between the cup bore and the tubular portion of the grommet would accumulate and be trapped in said channel.
In EP0.102.797, the stability of the grommet is ensured by giving the cup and grommet flange maching frustoconical geometries, which ensures a tight contact between at least part of the two surfaces even during use.
WO2009/042206 proposes to sandwich the flange of the rubbery grommet between the cup on its upper side, and a second metallic washer extending all the way from the top edge of the can to the upper surface of the base of the valve stem. This guarantees, beside an optimal stability of the grommet, that no moisture can diffuse through the material of the grommet. This solution is certainly very efficient to preserve the content of the can from moisture, but the cost of the can is rather high for a commodity product sold in such small containers/
WO96/17795 solves the problem of tightness between grommet and cup by injection moulding the grommet such as to embed a portion of the bore.
U.S. Pat. No. 5,762,319, US2010/147897, and U.S. Pat. No. 5,014,887 each discloses a valve cup comprising a substantially planar central portion joined to an intermediate peripheral rim by a substantially vertical wall, said substantially vertical first wall being provided with a fold extending over a substantial portion of the wall circumference. The intermediate peripheral rim is joined to a peripheral edge suitable for sealingly fixing the cup to the top opening of a container by a substantially vertical second wall. A grommet is coupled to the cup as follows.
A central hollow tubular portion of the grommet snugly fitting through a central bore located in the central portion of the cup, whilst a base portion of the grommet extends radially over the inner surface of the substantially planar central portion. A substantially vertical peripheral wall extends from the base of the grommet to mate the geometry of the substantially vertical first wall of the cup, with a groove mating the fold in said wall. This geometry ensure a good contact with between the grommet and the cup, but it has a number of drawbacks.
First, it is expensive because much material is needed to form the grommet base, as well as the cup. For pressure containers produced at a scale of several millions units per annum, any unnecessary waste of materials can cost a lot of money. Second, the geometry of the cup is very intrusive into the container, as it comprises two levels with two substantially vertical walls. It follows that for a same capacity, headspace comprised, a container comprising such bulky cups must be slightly larger than a container with a smaller cup design. Here again, a small waste of material multiplied by the production volume can results in high unnecessary production costs. Finally, because of the intricate interlocking of the grommet groove and the cup fold, both located on vertical walls, they cannot be assembled but, on the contrary, the grommet must necessarily be injected over the cup. Reducing the choice of processes for the production of such high volume item is necessarily a drawback for the user.
It can be seen that, although numerous solutions have been proposed to optimize aerosol valves suitable for dispensing polyurethane foams, there remains much to do to reduce the production cost and ensure at the same time an optimal stability and reliability of the valve. This and other problems are solved by the present invention as is described in continuation.